Rendering matcap with ambient occlusion using blender internal render and cycles
Enable the Ambient Occlusion in the World section of the properties panel. Set it to Add.

Create a new material: "Ambient".
Set the Diffuse Intensity to 1, and the Color to (1, 1, 1). Rendered view will show the ambient occlusion of the material.

Create a new material: "mixedMaterial". Assign it to the mesh.
Enable nodes, add the "Ambient" Material, the "Matcap" Material and combine them with a Color Mix node. Set the Mix nodes mode to Multiply.



This is the result.